The invention relates to a separable fastener system, an assembly method, and an assembly assembled thereby.
The technical field of the invention is that of assembling together an element, e.g. a vehicle window, and at least one other member, such as an accessory, by means of an intermediate structure such as a sealing gasket, or the like.
Numerous techniques exist for this purpose.
Document U.S. Pat. No. 2,367,657 describes hooking means for fixing a dashboard or a bumper to a car.
A rubber member is vulcanized on a metal sheet. Fasteners such as nuts and bolts are considered as being bulky, lengthy to install, and not stable.
In some cases, the length of a stud is slightly greater than the distance between a shoulder formed by a stud head and a flat, so that when forced into position, a compressed state is obtained.
Document GB-A-803 296 describes a releasable fastener such as a press stud, having a receptacle and a stud both of non-metallic material, for clothing.
Document DE-A-33 36856 describes a fixing element for vehicle upholstery, having two plastic portions that are elastically clipped together through an opening in the fixed portion, orifices being provided for a bolt.
Document DE-U-85 07 143 is cited as also relating to this technical field.
Document EP-A-214 459 describes a system for fixing building elements of plastics material on a thin support.
Document FR-A-2 593 445 describes a section member for fastening to the bodywork of a vehicle by resilient clipping, the section member having a longitudinally open tubular core of hard plastics material coextruded with a sealing gasket of soft plastics material, the cavity of the core being closed by a membrane that is likewise made of soft plastics material.
Document FR-A-2 691 759 describes a fixing system for fixing pieces to the structure of a motor vehicle, the system being implemented by directly molding a material that may reach 95 on the Shore hardness scale and may reach a bending modulus of 75 MPa.
A linking stud carrying the piece is provided with a recess constituted, going from the outside towards the inside, by an enlarged first portion outside towards the inside, by an enlarged first portion for putting the fixing member into place and forming locking means against rotation.
A cylindrical second portion forms a retaining duct for the fastener member. This second portion is advantageously tapped.
It opens out into a third portion formed by a an undercut snap-fastening chamber. The end wall of the chamber constitutes a material reserve and a screwing reserve for fixing members that are longer than the recess.
The connection between the stud and the member does not have any degree of freedom.
Document EP-A-593 909 describes a plastics fastener for a car.
It is provided with resilient fixing elements for securing the fastener in a receiving orifice in a portion of a metal sheet, in such a manner as to allow relative linear displacement to take place.
Because of the displacement, manufacturing tolerances can be compensated.
Known techniques suffer from drawbacks.
The main drawbacks are described in the particular example of overmolded window panels of the kind assembled to vehicle bodywork elements, e.g. in a car.
One technique consists in sticking the other member to the structure.
Means must be provided for holding the window in the fixing position while the adhesive is setting, e.g. by polymerizing. Such holding means are sophisticated and expensive. That slows down vehicle assembly.
Generally, the adhesives used make working conditions difficult and/or are unacceptable for the environment. In particular, harmful vapors are given off by the adhesives used.
Fixing obtained by adhesive is not separable. As a result, removing the window, whether when making a repair or at the end of the lifetime of the vehicle, for recycling purposes, is both difficult and not very effective.
On a window, the area on which the adhesive adheres needs to be masked by an opaque strip. This reduces the field of view through the window, and is often unsightly.
It is also common practice to provide fixing by means of screws that are secured to the bodywork and that are also engaged in tapped nuts or inserts, themselves secured to the gasket of the window.
As with adhesive, this requires means to be placed in the mold, and such means are likewise sophisticated and expensive.
In addition, a nut used as an insert gives rise to a risk of the entire molding being discarded, particularly as a result of damage that occurs when closing the mold.
Often, an unacceptable amount of space needs to be provided for receiving such inserts, in particular in the thickness direction perpendicular to the window.
Such inserts increase costs and make logistics more complicated, particularly because of the need to package and ship additional pieces.
The invention seeks to solve these drawbacks, in particular.
It makes it possible to limit the number of pieces required for fixing purposes, to make them more compact, and to simplify the logistics that need to be provided.
By means of the invention, it is possible to obtain fixing that is reliable, with limited risks for the environment, while making assembly both separable and easy, e.g. for ultimate recycling.
To this end, the invention provides, in a first aspect, a separable fastener system for assembling an element, e.g. a vehicle window, to at least one other member, such as a vehicle accessory or a bodywork frame, via an intermediate structure, e.g. a sealing gasket, or the like.
Consideration is given mainly to two applications of the invention.
Either assembly requires the element to be fastened to the other member, as is the case for a window being fastened to vehicle bodywork.
Or else the other member is fastened to the element, as is the case of an accessory, e.g. a brake light fastened to a vehicle window.
The system comprises in combination:
a structure of elastically deformable material;
intermediate fixing means for fixing the structure securely to the element, for example a shape that is complementary to the shape of a corresponding portion of the element;
at least one positioning and/or sealing surface on the structure for placing against the said other member;
at least one stud on the structure flush with and/or projecting from the positioning surface, close to said surface and/or including said surface; the stud being designed to be engaged with clearance in a recess of the said other member;
at least one expansion space formed around the stud; and
at least one orifice in the stud extending in an insertion direction and provided with a cylindrical housing of substantially circular cross-section ad extending substantially rectilinearly along the insertion direction.
The housing is designed to hold captive in the structure the shank of a separate fastener means such as a screw or the like, that shank having a rounded chamfer thread of cross-section at its root that is substantially equal to or greater than that of the housing when in a ready position, i.e. when at rest before insertion of the shank.
As a result, the stud is suitable for having the shank inserted therein and for being subjected to predetermined outwards elastic deformation or swelling into the expansion space without injuring the orifice of the housing, and for being pressed outwards against the inside of the recess.
According to a characteristic, the intermediate structure is made of an elastically deformable material such as rubber, polyurethane known as xe2x80x9cPUxe2x80x9d, or a polymer, in particular the ethylene and propylene terpolymer known as xe2x80x9cEDPMxe2x80x9d.
By way of example, the material used may have hardness on the Shore D scale of the order of 50 to 85, and a Young""s modulus of the order of 250 MPa.
The intermediate structure may constitute a single block, for example, in particular a block that is molded directly on the element.
According to another characteristic, the intermediate fixing means include at least one bearing plane designed to be placed against (and optionally glued to) a face of the element and/or a concave shape designed to receive (flush) a complementary convex edge surface of the element. For example, these intermediate means may be integrally molded with the intermediate structure.
According to yet another characteristic, the structure includes at least one positioning surface such as a bearing strip designed to be substantially parallel to a face of the said other member and/or a sealing surface such as an elastically deformable lip designed to be placed against the said other member.
In an embodiment, the intermediate structure is provided with at least one stud whose free end is flush with a positioning surface, and includes such a surface.
For example, the orifice of the stud opens out in the insertion direction, at least in a positioning surface and/or the expansion space is defined exclusively by the outline of the stud, perpendicular to the insertion direction.
In another embodiment, the intermediate structure is provided with at least one stud projecting from a positioning surface, in the vicinity thereof, and is at least locally separated therefrom perpendicularly to the insertion direction by the expansion space.
For example, the outline of the stud may be designed to swell into a ring shape, thereby forming a positioning surface portion by surrounding and/or providing sealing between an end wall of the expansion space and the recess in the said other member.
According to a characteristic, the expansion space includes an end wall that is substantially perpendicular to the insertion direction.
For example, at least one stud of the intermediate structure is frustoconical in shape, of cross-section that is larger in area close to the end wall of the expansion space than where the orifice opens out at its end that is opposite in the insertion direction.
The frustoconical shape may possible be designed to allow its flare angle to increase during predetermined outward elastic swelling.
According to another characteristic, at least one orifice is provided with a rectilinear cylindrical longitudinal housing that is substantially parallel to the insertion direction. For example, the housing need not have any undercut.
In an embodiment, the orifice includes an end gap or opening to enable a shank of separate fastener means to have its free end when in a clamping position at a distance in the insertion direction from an end wall or opening.
According to yet another characteristic, the system includes separate fastener means such as screws or the like, each having a threaded shank designed to be held captive, in the insertion direction, in a housing of the structure.
The diameter at the root of the thread on the shank is substantially equal to or greater than the inside diameter of the housing when in a ready position, i.e. before the shank is inserted.
The shank may be made of synthetic material or of metal. Such a shank differs from a xe2x80x9cself-tappingxe2x80x9d shank since a self-tapping shank injures its assembly housing, and therefore weakens it.
The thread has a rounded chamfered profile, and for example in section parallel to the insertion direction, and going from its insertion free end to its opposite end, may comprise:
a straight leading edge of the thread that slopes outwards substantially at 45xc2x0;
a rounded junction between edges having a radius that is about 0.2 times to 0.3 times the diameter at the root of the thread, and in particular about 0.25 times the diameter, and/or that is greater than 2 mm or 3 mm; and
a straight retaining edge of the thread, that slopes inwards substantially at 15xc2x0 to a transverse plane.
In a second aspect, the invention provides a method of assembling together an element such as a vehicle window and at least one other member such as an accessory or a bodywork frame, via an intermediate structure, e.g. a sealing gasket provided with at least one separable fastener system as mentioned above.
The invention comprises in particular, the following combination of steps:
inserting a shank of separate fastener means in an insertion direction into a stud housing, using force and screwing motion;
subjecting the stud under the effect of the insertion force solely to a predetermined amount of elastic swelling, without injuring it;
locking the stud under the effect of the swelling into the expansion space bearing outwards against the inside of a recess in the other member; and optionally
subjecting a frustoconical shape of the stud to an increase in its flare angle during the predetermined outward elastic swelling.
When the orifice includes an end gap or opening, the shank of the separate fastener means, when in its final clamping position, has its free end at a distance in the insertion direction from an end wall or an opening.
According to a characteristic, the outline of the stud is swollen into a ring, thereby forming a portion of a positioning surface that acts by clamping and/or sealing between an end wall of the expansion space and the recess in the other member.
In a third aspect, the invention provides an assembly assembled using at least one fastener system and/or assembly method as defined above.
In an embodiment, the assembly comprises at least: an element, e.g. an element that is flat in the insertion direction, such as a window; a gasket or the like at the periphery of the element, e.g. a sealing gasket including at least one separable fastener system; and one other member such as a vehicle bodywork frame.
In an embodiment, the assembled assembly comprises at least: one other member, e.g. an accessory such as a brake light; an element such as a window, e.g. a motor vehicle back window; and an intermediate structure fixed at a distance, perpendicular to the insertion direction from the edges of the element.